PRG4 and rheumatoid arthritis: The genes were KEGG-annotated and categorized as focal adhesion (hsa04510, p-value = 0.002), neuroactive ligand-receptor interaction (hsa04080, p-value = 0.072), mitogen-activated protein kinases (MAPK) signaling pathway (hsa04010, p-value = 0.090), etc. We further set the threshold of false discovery rate (FDR)-adjusted p-value at 0.05 and specified at least 2-fold change, and found that PRG4 was significantly downregulated in RA, compared with OA.